Hey sir_root!
At week 11, seeing some yellowing on the lower leaves is usually just the natural "fade" as the plant pulls mobile nutrients like Nitrogen toward the buds. Since you’re running hot soil with no added nutes, she’s likely just reaching the end of the soil's fuel supply. Sulfur issues usually start at the top on new growth, so if it's just a few bottom leaves, it's definitely not a lockout. Just keep an eye on your pH as you planned, but it sounds like she’s just ripening up perfectly.
Happy Growing, Growmie!